1. Field of the Invention
The invention relates to a disc brake rotor, and more particularly toward a vented rotor configured to attenuate brake squeal noise.
2. Related Art
A rotor for a disc brake forms part of the vehicle braking system and rotates together with a wheel. The rotor has a pair of opposed friction surfaces against which brake pads are brought into contact to arrest rotation of the wheel. In many applications, the rotor section of the disc brake is ventilated between the friction surfaces to improve cooling characteristics by dissipating heat produced from friction during the braking process. Ventilated rotors are normally arranged so that a plurality of radially extending vent holes are formed between inboard and outboard friction plates, with structural ribs defining the sides of each vent hole.
In such arrangements, the ventilated rotor exhibits numerous vibration modes. Certain vibration modes will have a larger amplitude than others, and when the large amplitude modes occur at certain audible frequencies, in conjunction with an excitation input of like frequency, an objectionable squealing noise may be heard. The distinctive high-pitched sound of brake squeal is a friction-induced dynamic instability that is notoriously difficult to predict. Numerous variables are thought to contribute to brake squeal, including brake pressure, temperature, rotor speed, and deceleration. Other variables thought to possibly contribute to brake squeal include dust accumulation, deterioration of damping layers, variation of friction materials and contact conditions.
When the operator of a vehicle applies the brakes, a portion of the braking energy turns into vibration energy. Squeal occurs even in new vehicles when system instability causes the vibration to be self-excited, and the vibration amplitude rises increasingly higher. Although brake squeal is not indicative of a defect in the braking system, a perception of a mechanical problem is created, or a presumption that the brake has been poorly made. This negative consumer impression, albeit falsely based, is particularly harmful to vehicle manufacturers, dealers, and the makers of braking systems. Design engineers have sought to address the problem of brake squeal through various techniques and analytical methods. However, because of the numerous variables thought to contribute to brake squeal, this is a notoriously challenging endeavor.
A more recent approach addressing brake squeal has relied upon an analysis procedure known as the “complex eigenvalue method” to diagnose the problem. The purpose of this method is to calculate the dynamic instability of the system due to both modal coupling and velocity-dependent friction. A complex eigenvalue analysis method is an iterative process involving commercially available software where a brake engineer may suggest a solution that involves modifying component geometry to shift natural frequencies, trying new materials or different damping treatments, or adding new devices to change boundary conditions or contact conditions. User experience and engineering judgment are essential to obtain favorable results using the complex mode analysis, and in recent years many efforts have been made to increase the predictability of the complex eigenvalue method.
Notwithstanding the usefulness of the complex eigenvalue method as a diagnosis tool, design engineers still do not fully understand the underlying mechanisms which cause brake squeal, and as a result continue searching for new and improved solutions that will completely, or at least substantially, eliminate the objectionable audible frequencies at the root of brake squeal.